An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NO). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is typically removed upstream of the exhaust gas driven turbine 1126 associated with the turbocharger. For example, in many EGR applications the exhaust gas is diverted directly from the exhaust manifold and diverted via an EGR conduit to the intake system. Likewise, the recirculated exhaust gas may be re-introduced to the intake air stream downstream of the compressor and inter-cooler or air-to-air aftercooler.
At many engine operating conditions within a turbocharged diesel engine, there is a pressure differential between the intake manifold and the exhaust manifold which essentially prevents many such simple EGR systems from being utilized. For example, at low speed and/or high load operating conditions in a turbocharged engine, the exhaust gas does not readily flow from the exhaust manifold to the intake manifold. Therefore many EGR systems include an EGR driver such as a Roots-type blower or an auxiliary compressor to force the exhaust gas from the exhaust manifold to the higher pressure intake manifold. See U.S. Pat. No. 5,657,630 (Kjemtrup et al.) issued on Aug. 19, 1997 as merely one example of the many EGR systems that utilize a pump or blower type arrangement to drive the EGR from the exhaust manifold to the intake: system. See also European Patent No. EP 0 889 226 B1 published Aug. 8, 2001 as well as PCT patent document WO 98/39563 published Sep. 11, 1998 that disclose the use of an auxiliary compressor wheel driven by the exhaust gas driven turbine associated with the turbocharged diesel engine. The auxiliary compressor wheel forcibly drives the recirculated exhaust gas from the exhaust manifold to the intake system at nearly all engine operating conditions.
One apparent problem with such forced EGR systems that utilize an auxiliary compressor is that the auxiliary compressor chokes long before the EGR flow requirements are met at many light load operating conditions. Such light load yield conditions where the exhaust manifold pressure and the auxiliary compressor, blower, pump or other EGR driver is more of a flow restriction than an assist.
It may be preferred to reintroduce exhaust gases upstream of the compressor as disclosed in U.S. Pat. No. 6,651,618 (Coleman et. al) issued on Nov. 25, 2003. Coleman discloses a low pressure EGR system that utilizes a throttle valve to control air and recirculated gases being delivered to the engine, and an EGR valve to control the amount of exhaust gases that are being reintroduced into the intake. Because exhaust gases are at a higher pressure than intake air in a low pressure EGR systems, the need for the aforementioned blower or compressor in the commonly used high pressure EGR system is eliminated. This does, however, require a means of injecting the exhaust gases into the intake. One such injecting means is found in U.S. Pat. No. 5,611,204 (Radovanovic et al.) issued on Mar. 18, 1997, which discloses various injector designs.
One apparent problem with the utilization of the throttle valve is the inefficiency caused from airflow restriction resulting from the throttle valve. Such a restriction increases the pressure and airflow loss, which may lead to choking the engine. This may result in a decrease in the fuel economy of the internal combustion engine. The performance of the EGR system is based on how much exhaust gas it can draw into the engine with minimal airflow and pressure loss. In addition, the reliability and durability of such a throttle valve is suspect to failures due to the mechanical nature of such devices.
The present invention is directed to overcoming one or more of the problems as set forth above.